Diaphragm valves for use in irrigation systems commonly have an inlet passage, an outlet passage, and a diaphragm positioned to selectively open and close a generally cylindrical diaphragm seat to permit or block fluid flow from the inlet passage to the outlet passage. A control chamber is positioned on the opposite side of the diaphragm from the seat to control the position of the diaphragm relative to the seat.
When the fluid pressure acting on the diaphragm from the control chamber side exceeds the fluid pressure acting on the opposite side of the diaphragm, the diaphragm will be forced against the seat to block fluid flow through the seat and thereby block fluid flow from the inlet passage to the outlet passage.
Conversely, when the fluid pressure acting on the diaphragm from the control chamber side is less than the fluid pressure acting on the opposite side of the diaphragm, the diaphragm will be forced away from the seat to permit fluid flow through the seat and thereby permit fluid flow from the inlet passage opening to the outlet passage.
As the diaphragm moves from the open position to the closed position, the distance, and in turn the flow area, between the seat and the diaphragm continually decreases until the diaphragm engages the seat to block flow through the seat. The bottom surface of the diaphragm commonly has an annular portion designed to engage an annular seat. In the closing operation, the diaphragm typically lowers straight onto the seat so that the entire annular portion engages the seat relatively simultaneously. The final portion of the closing movement causes an abrupt change in the flow area between the diaphragm and the seat and, consequently a sudden pressure spike greater than the upstream pressure. More specifically, the abrupt conversion of the motion energy in the flowing fluid to pressure energy acting on the components of the diaphragm valve can cause a pressure spike in the upstream pressure. Pressure spikes are known to cause the diaphragm valve to experience a water hammer effect, which can undesirably result in increased stress on the components of the diaphragm valve, as well as other components of the irrigation system. Overall, this can lead to premature wear or failure of the components.
In order to control the pressure in the control chamber, the valve typically has a fluid entrance path to, and a fluid exit path from, the control chamber. The fluid entrance path may extend between the inlet passage and the control chamber and may be continuously supplied with fluid from the inlet passage. The fluid exit path may extend between the control chamber and the outlet passage. A selectively actuable control valve or actuator may be positioned to block and permit fluid flow through the fluid exit path.
When the control valve is positioned to block fluid flow through the fluid exit path from the control chamber, the fluid entrance path continues to permit fluid to flow from the inlet passage to the control chamber, thereby causing fluid to accumulate in the control chamber. The diaphragm has a larger surface area exposed to pressure on the control chamber side than is exposed to high pressure on the side facing the inlet passage. Thus, when the fluid pressure in the control chamber and inlet passage are generally the same, the operation of the fluid pressure in the control chamber acts on the greater surface area of the control chamber side of the diaphragm and causes the diaphragm to either shift from the open position to the closed position or remain in the closed position.
When the control valve is positioned to permit fluid flow through the fluid exit path from the control chamber, fluid exits the control chamber at a faster rate than fluid enters the control chamber. This causes the fluid pressure acting on the control chamber side of the diaphragm to decrease relative to the fluid pressure acting on the side of the diaphragm facing the inlet passage. The fluid pressure in the inlet passage then causes the diaphragm to move to the open position, whereby the diaphragm is spaced from the seat and fluid flow is permitted from the inlet passage, through the seat and out the outlet passage.
The flow path that the fluid follows when the diaphragm valve is in the open position is generally from the inlet passage, through the diaphragm seat, and finally out through the outlet passage. As the fluid follows this path, internal geometry of the diaphragm valve and valve housing can cause very rapid acceleration and deceleration of the fluid. Specifically, in reverse flow, upright diaphragm valves, a cylindrical wall forms an annular diaphragm seat and a passage from the inlet leads to an annular cavity between the cylindrical wall and the outer wall of the valve. The entrance to the annular cavity typically has a reduced flow area between the end of a wide inlet passage and the cylindrical wall which can cause acceleration of the fluid upon entering a smaller area from the larger inlet passage. Simultaneously, this intersection forces some of the incoming flow to turn upward to the valve seat and directs some of the incoming flow to the lateral sides and to the downstream side of the annular cavity before flowing upward to the seat. Such geometry of upright valves and internal flow path therein can lead to rapid turning of the fluid flow, thereby accelerating the flow, in a vector sense (or in other words negative acceleration or deceleration), by forcing it to change direction several times.
This undesirable acceleration and deceleration may be compounded during the transition periods between the open and closed positions depending on the way the diaphragm shifts relative to the seat. Particularly, for diaphragms that lift straight off of the seat, or in other words generally vertical, the seat draws a significant amount of water from the outlet side of the seat thereby maintaining a relatively high acceleration of the flow at least during the transition between the open and closed positions of the valve.
Further, while these known diaphragms are designed to lift straight upward, the varying forces and pressures on the diaphragm can cause the diaphragm to slightly tilt as it lifts upward affecting pressure loss in undesirable ways. In one case, since the downstream side of the annular cavity creates a dead end where the fluid is redirected back toward the valve seat, this structure causes stagnation and relatively high fluid pressure at the downstream side of the annular cavity. The high pressure may result in the diaphragm lifting with an undesirable tilt where the downstream side of the diaphragm lifts higher than the upstream side. Such tilting in undesirable directions can cause turbulence and pressure loss.
In addition, the geometry of the diaphragm seat itself can cause additional acceleration of the fluid as it approaches the opening of the seat from the entrance area of the inlet cavity. This can be due to the larger flow area of the inlet opening or the inlet cavity as compared to the flow area of the opening of the seat, which can cause the fluid to rapidly accelerate as it approaches the opening in order to maintain conservation of mass in the incompressible flow. Moreover, the geometry of the seat can cause deceleration of the fluid at it exits the opening of the seat and enters the outlet opening due to the smaller flow area of the opening of the seat as compared to the larger flow area of the adjacent portion of the outlet opening.
Such varying flow, with rapid acceleration and/or deceleration of the flow, whether through a change in flow area or flow direction, can cause the loss of energy in the fluid, which results in a pressure loss in the diaphragm valve and can therefore increase the number of valves required to irrigate the intended area.
In view of the foregoing, there remains a need for diaphragm valves having improved flow, including the reduction of energy lost during flow.